The aim of our project is to precisely define the interferon gamma receptor (IFNgammaR) 2 recycling domain and the biologic effects of IFNgammaR2 modulation. Human disease and animal models show a broad and diverse spectrum of clinical phenotypes associated with differential IFNgamma receptor display and responsiveness. Increased susceptibility to infections, predominantly mycobacteria, but also including bacteria, virus and fungi; autoimmune disease pathogenesis; and tumor generation and control are all conditions associated with differential IFNgamma responsiveness and IFNgamma receptor display. The IFNgammaR complex is composed of four molecules, two IFNgR1 and two IFNgR2. After binding the IFNgammaR complex, IFNgamma triggers a broad spectrum of biological effects. While the IFNgammaR1 is constitutively expressed on all nucleated cells, IFNgammaR2 membrane display is quite limited and tightly regulated, creating a bottleneck in IFNgamma responsiveness. Several groups have hypothesized the existence of a recycling domain in IFNgammaR2, similar to what has been demonstrated in IFNgammaRI. We have identified the discrete amino acids in the intracellular domain of IFNgammaR2 that mediate its recycling, and lead to plasma membrane over-accumulation when altered. Truncation of the receptor immediately upstream of the recycling domain, or deletion or substitution of the sequence of the amino acids involved in the recycling domain, have enabled us to create dominant negative and dominant gain of function IFNgammaR2 mutants, respectively. These results are the first physical evidence of the existence of an IFNgammaR2 recycling domain and the first demonstration of dominant negative, as well as dominant gain of function mutations in IFNgammaR2. This research project is designed to understand how modulation of the IFNgammaR2 recycling domain affects IFNgamma signaling, IFNgamma receptor trafficking, IFNgamma mediated apoptosis, and immune-mediated cytotoxicity towards cells expressing IFNgammaR2 mutants. We expect that by exploring the fate of IFNgammaR2, the molecule described as the bottleneck in IFNgamma responsiveness, we will expand our knowledge of the immune system, the way it controls external infectious challenges, the immune mediated generation of certain diseases, and some of the mechanisms of the immune control of cancer.